Grilled Burgers with Horseradish Sauce

Ingredients

• 1/2 cup reduced-fat sour cream
• 1 tablespoon snipped fresh dill or 1 teaspoon dill weed
• 1 tablespoon finely chopped onion
• 1 tablespoon sweet pickle relish
• 2 teaspoons prepared horseradish
• BURGERS:
• 3/4 cup chopped fresh mushrooms
• 1/4 cup shredded carrot
• 1/4 cup finely chopped onion
• 2 tablespoons minced fresh parsley
• 1 tablespoon Worcestershire sauce
• 1/2 teaspoon salt
• 1/4 teaspoon hot pepper sauce
• 1/8 teaspoon pepper
• 1-1/4 pounds lean ground beef (90% lean)
• 6 whole wheat hamburger buns, split
• 6 lettuce leaves
• 12 tomato slices